It has been known that a phenomenon wherein a photo-current generated by a larger number of electrons than the number of incident photons is observed (photo-current multiplication phenomenon) when a layer composed of a photo-conductive organic semiconductor is contacted to a conductive layer composed of a material different from the photo-conductive organic semiconductor (such as a metal, an organic semiconductor and an inorganic semiconductor) (heterogeneous material conductive layer), and the layer composed of a photo-conductive organic semiconductor is irradiated by light while applying a voltage (refer to Non-Patent Document 1 and Patent Document 1).
This is a phenomenon wherein the electric charge of one in electron-hole pairs formed by light irradiation (e.g. holes) is accumulated in a photo-conductive organic semiconductor in the vicinity of the boundary between the layer composed of the photo-conductive organic semiconductor and the heterogeneous material conductive layer by light irradiation, and a large amount of charge (e.g. electrons) having a polarity opposite to the accumulated charge is injected by tunneling from the heterogeneous material conductive layer into the photo-conductive organic semiconductor by the high electric field formed by the charge. An element having a combination of a layer composed of a photo-conductive organic semiconductor and a heterogeneous material conductive layer using such a phenomenon is herein referred to as a photo-current multiplication element.
As a device to which a photo-current multiplication element is applied, there has been known an organic light-light conversion device having:
a light sensing unit having a layer including a photo-conductive organic semiconductor that causes a photo-current multiplication phenomenon by light irradiation (photo-current multiplication layer); and
a light emitting unit having a layer including an electroluminescent organic semiconductor that emits light by current injection (organic EL light emitting layer).
In such a device, although light is emitted from the light emitting unit by radiating light to the light sensing unit, the light is amplified by radiated light, and the wavelength thereof can be the same as or different from the wavelength of the radiated light.
As examples of such organic light-light conversion devices, there has been known:
a device wherein a light sensing unit having a layer including a photo-conductive organic semiconductor and a light emitting unit having a layer including an electroluminescent organic semiconductor are integrally laminated on the same substrate (Non-Patent Document 2); and
a device wherein a light sensing unit having a layer including a photo-conductive organic semiconductor and a light emitting unit having a layer including the above-described organic electroluminescent body placed on a location different from the location of the light sensing unit on the same substrate (Non-Patent Document 3).
Both the photo-conductive organic semiconductor and the electroluminescent organic semiconductor used in the photo-current multiplication layer and an organic EL light emitting layer in these devices were low-molecular-weight compound, such as organic pigments, and these were used alone or by dispersing in a resin in these layers.
Patent Document 1: JP-A-2002-341395
Non-Patent Document 1: M. Hiramoto, T. Imahigashi and M. Yokoyama: Applied Physics Letters, Vol. 64, 187 (1994)
Non-Patent Document 2: “Applied Physics”, Vol. 64 (1995), 1036
Non-Patent Document 3: 49th Lecture Meeting of Japan Society of Applied Physics, 28p-M-10